I am wondering how much effect does air temp has on our 2.0 N/A engine. I can't help noticing that my P5 runs smoother and has better throttle respond in a cool morning. I guess that's why we want those ram air intakes... Or am I hallucinating...?

 

No, it's not your hallucination. Cold air has a higher oxygen density, so combustion is better when you have cold air going into the engine, so you have more power. And that's the advantage of installing CAIs besides getting more flow.

 

I would rephrase that to:

Colder air has a higher density. Thus there are more molecules of oxygen in a cubic foot of cold air than there are in a cubic foot of hot air. So, there are more molecules of oxygen available to combust with the hydrocarbons you inject in to the cylinder, thus creating a more efficient combustion reaction.

Also cold air reaches a higher pressure than warm air in your cylinder. Say every cubic foot of air is compressed 7:1. That cubic foot of air will become 1/7 a cubic foot of air inside the cylinder. The more molecules there are bouncing around on the edges, thus creating pressure, the higher the pressure will be. Kind of a cheap turbocharger although the pressures never reach anywhere near the level a forced induction system can provide.

I could keep going but I'll stop here.